Cited as a means for obtaining a radiographic image for medical diagnosis or non-destructive testing of various types of tissue and applying it to diagnosis and radiographic flaw detection are: radiography by a combination of a silver halide photographic light sensitive material and a radiographic intensifying screen, or a radiographic image conversion method by the use of a stimulable phosphor from which, after absorption of radiation energy, the accumulated radiation energy is emitted in the form of fluorescence by stimulation with electromagnetic waves such as visible light or infra-red rays (hereinafter referred to as stimulable phosphor).
Diagnosis or examination with radiography is such that radiation transmitted through or emitted from photographic object is converted, through absorption by phosphor contained in the radiographic intensifying screen and its excitation, into visible light, which produces a radiographic image on a silver halide photographic light sensitive material. The radiographic image is formed by exposing, to radiation through an object, the silver halide photographic light sensitive material having, on one side or both sides of a support, a silver halide emulsion layer, which is in contact with a radiographic intensifying screen to radiation through an object.
The phosphor has a high brightness and can form a radiographic image with a relatively small dose of radiation, so that exposure to radiation by the object is minimal. It is well known that sharpness and graininess of such images depend upon the particle size and dispersion and homogeneity of the phosphor, and in particular upon the filling ratio in the phosphor containing layer.
The radiographic image conversion method employing stimulable phosphor includes the employment of a radiation image converting panel containing the stimulable phosphor (hereinafter, referred to as a stimulable phosphor panel). In this case, the radiation transmitted through or emitted from the object is absorbed by a stimulable phosphor contained in the panel, followed by stimulating time-sequentially the phosphor with electromagnetic waves such as visible light or infra-red rays (also known as stimulating light), and emitting the radiation energy accumulated in the phosphor, in the form of light (photo-stimulated luminescence). The photo-stimulated luminescence is read as electric signals and based on the electric signals obtained, the object or its radiographic image is reproduced as a visible image. The panel which has already been read is treated to eliminate all residual images and made ready for the next photograph. Thus, the conversion panel can be employed repeatedly.
Similarly to the screen brightness, bending strength and abrasion resistance of the panel are also dependent upon dispersibility, homogeneity and filling ratio of the stimulable phosphor. Of these, the filling ratio of the stimulable phosphor is particularly influential.
Means for enhancing emission characteristics of the screen and panel is in general to enhance the filling ratio of the phosphor.
JP-A 3-21898 (herein, the term, JP-A means unexamined and published Japanese Patent Application) described, as a means for enhancing the filling ratio, the use of a resin having a glass transition temperature (hereinafter, denoted simply as Tg) of 30 to 150.degree. C. and a radiation image converting panel with 70% or more filling ratio of a stimulable phosphor, which was achieved by compressing a phosphor containing layer (hereinafter, also denoted as a coating layer). Since the radiographic intensifying screen or the radiation image converting panel is employed with being rubbed with a photographic film or roll at room temperature, the Tg of a resin to be used is preferably not less than 30.degree. C. However, when a resin with a high Tg is employed as a binder, the coating layer is not easily reduced in volume during drying, leading to a decreased filling ratio. Further, when the resulting coated layer is subjected to compression, due to deteriorated softening characteristics, the phosphor is under pressure liable to produce defects or destruction of the crystal structure, resulting in lowering of the sensitivity. Furthermore, the compression temperature needs to be raised to transform the resin, producing problems such as lowered manufacturing efficiency.
Accordingly, there is desired a radiographic intensifying screen or a radiation image converting panel with superior brightness and excellent image quality, and a manufacturing method thereof.